1. Field of the Invention
Embodiments of the present invention relate generally to a multi charged particle beam writing apparatus and a multi charged particle beam writing method, and more specifically, to an apparatus and method that corrects an error (AU error) generated due to being rounded to a minimum unit of the AU (address unit) in execution of data conversion.
2. Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. For forming a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a high-precision master pattern.
FIG. 9 is a conceptual diagram explaining operations of a variable-shaped electron beam writing or “drawing” apparatus. The variable-shaped electron beam writing apparatus operates as described below. A first aperture plate 410 has a quadrangular aperture 411 for shaping an electron beam 330. A second aperture plate 420 has a variable shape aperture 421 for shaping the electron beam 330 having passed through the aperture 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the aperture 411 is deflected by a deflector to pass through a part of the variable shape aperture 421 of the second aperture plate 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g., x direction) during writing. In other words, a quadrangular shape that can pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the x direction. This method of forming a given shape by letting beams pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) system.
First, when layout data (design data) where figure patterns to be written are arranged is generated, the layout data is converted into writing data having a format which can be input to the writing apparatus. Then, when the writing data is input to the writing apparatus, data conversion processing of a plurality of steps is performed for the writing data so that a figure pattern defined in the writing data may be divided into a plurality of shot figures each of which can be irradiated by one beam shot. A design figure pattern defined in the layout data is written on the target object by combining such a plurality of shot figures. In a series of processing described above, since a deviation of an AU (address unit) occurs regarding a figure size in the data when comparing the AU before and after some data conversion processing, an error because of an AU error which occurs due to being rounded to a minimum unit being the AU (address unit) occurs regarding the size of each shot figure to be finally written when data conversion is performed. Consequently, against the size of a figure pattern defined in layout data, an error occurs in the size of a figure pattern to be finally written. It is difficult to directly correct AU errors. Conventionally, since the amount of the size of such an error can be relatively ignored compared to the shot size, it has not been taken into account. However, along with recent miniaturization of patterns, the shot size is also becoming miniaturized.
In the electron beam writing, a phenomenon called a “proximity effect” occurs when electron beams irradiate a mask with resist to write or “draw” a circuit pattern thereon. The proximity effect occurs by backscattering of electron beams penetrating the resist film, reaching the layer thereunder to be reflected, and entering the resist film again. As a result, a dimensional variation occurs, that is, a written pattern is deviated from a desired dimension. In order to avoid this phenomenon, a proximity effect correction operation that suppresses such dimensional variation by, for example, modulating a dose is performed in the writing apparatus.
In the conventional proximity effect correction operation, the size of a shot figure to be finally written has not been taken into account. However, with the current tendency of miniaturization of shot sizes, the influence of AU errors on the proximity effect is increasing. Therefore, even if the proximity effect correction operation to modulate the dose is performed by the conventional method, there is a problem that a correction residual error occurs regarding the proximity effect correction.
There is disclosed a technique where resizing is performed for a shot figure by using a resizing value predetermined according to the size, and the amount of proximity effect correction is calculated based on the resized shot figure (e.g., refer to Japanese Patent Application Laid-open (JP-A) No. 2012-019066). However, in the first place, AU errors are difficult to resize, and therefore, it is difficult to solve the problem described above even by using this technique.